Currently, in the world, energy is used mostly in irreversible manners to thermal energy. In order to prevent such thermal energy from being exhausted or to remove the exhausted thermal energy, forced air cooling or forced cooling utilizing energy supplied by an additional heat engine or electric energy is carried out. This causes an increase in energy consumption, and noises generated in such cooling device, and thereby causes problems.
Also when the temperature of a building or regions surrounding it is high under the influence of radiation of sunlight, geothermal heat, etc., forced air cooling or forced water cooling utilizing energy supplied by an additional heat engine or electric energy is carried out in order to exhaust or remove the thermal energy of this section of high temperature. This causes an increase in energy consumption, and noises generated in such cooling device, and thereby causes problems.
However, currently, the effort to reduce loads to the environment by saving energy by actively recycling such thermal energy, or by reducing noises, has been just started. The technique to recycle actively generated thermal energy without additional use of thermal or electric energy is not yet completed. Moreover, the noises generated in cooling devices, etc. are not yet reduced sufficiently.
Although thermal energy exists inexhaustibly in the natural world as described above, the technique to take out the thermal energy in the form of electric energy or chemical energy is still in an initial stage of development far from practical use.
However, conversion from thermal energy to electric energy, and conversely from electric energy to thermal energy, is possible according to principles of physics which has been known as Peltier effect and Seebeck effect for a long time. That is, radiating or absorbing heat is produced other than Joule heat, when current flows through conductors of two different kinds which are connected and held at a uniform temperature. This effect is the phenomenon first discovered by J. C. A. Peltier in 1834, and called Peltier effect. Moreover, when conductive wires of two different kinds are connected, the two contact points are held at different temperatures T1 and T2, and one of the conductive wires is cut, then an electromotive force is produced between the cut ends. This phenomenon was first discovered by J. J. Seebeck in 1821. The electromotive force generated between the two ends is called thermal electromotive force, and this phenomenon is called Seebeck effect in honor of the discoverer. In other words, the Peltier effect is a principle of conversion from electricity to thermal energy, while the Seebeck effect is a principle of conversion from thermal energy (temperature difference) to electric energy.
The development of a thermoelectric conversion element (Seebeck element) utilizing the Seebeck effect is attracting attention as substitute energy for fossil fuel and atomic power. The thermo-electromotive force of the Seebeck element is dependent on the temperatures of the two contact points, and moreover on the materials of the two conductor wires. A derivative value obtained by dividing the thermo-electromotive force by a temperature variation is called Seebeck coefficient. The thermoelectric conversion element is formed by contacting two conductors (or semiconductors) different in the Seebeck coefficient. Due to difference in the number of free electrons in the two conductors, electrons move between the two conductors, resulting in a potential difference between the two conductors. If thermal energy is applied to one contact point, the movement of free electrons is activated at the contact point, but the free electron movement is not activated at the other contact point being provided with no thermal energy. This temperature difference between the contact points, that is the difference in the activation of free electrons, causes conversion from thermal energy to electric energy. This effect is generally referred to as thermoelectric effect.
In general, the Seebeck element is an integrated element of a heating portion (higher temperature side) and a cooling portion (lower temperature side). A thermoelectric conversion element utilizing the Peltier effect (referred to as “Peltier element”) also is an integrated element of a heat-absorbing portion and a heat-generating portion. Accordingly, the heating portion and the cooling portion interfere with one another in the Seebeck element, while the heat-absorbing portion and the heat-generating portion interfere with one another in the Peltier element. As a result, the Seebeck effect or the Peltier effect decays with time. Therefore, it is impractical to construct large-scale energy conversion equipment with such Peltier element and Seebeck element, because physical restriction is imposed by the place where the equipment is disposed.
The inventor (applicant) of the present application has invented and proposed a thermoelectric conversion apparatus utilizing the Seebeck effect and an energy conversion system utilizing this (cf. patent document 1). According to patent document 1, a circuit system constructed with the Seebeck element or the Peltier element is limited to a system including an external power supply, and used in limited forms.
FIG. 10 is a schematic diagram showing a long distance thermal energy transfer system utilizing the Peltier effect which has been proposed in patent document 1 by the inventor (applicant) of the present application. As shown in FIG. 10, two thermoelectric conversion elements 100 and 200 are provided so as to face one another. Each thermoelectric conversion element 100 (200) is constructed by joining together a first conductive member A101 (A201) and a second conductive member B102 (B202) having different Seebeck coefficients by a joining member d103 (d203) made of a material having a high thermal conductivity and electrical conductivity (for example, copper, gold, platinum, and aluminum).
The surface of the first conductive member A101 and the second conductive member B102 of the thermoelectric conversion element 100 which are opposed to the joining member d103, and the surface of the first conductive member A201 and the second conductive member B202 of the thermoelectric conversion element 200 which are opposed to the joining member d203, are connected by a conductive material having a high thermal conductivity (a wiring material made of copper, gold, platinum, aluminum, etc.), respectively. An external direct-current power supply 300 (Vex) is provided on the line connecting the first conductive members. A paired Peltier effect heat transfer electric circuit system is thus provided, having the joining members d103 and d203 as the heat-absorbing side and the heat-generating side, respectively.
The length of the above-described conductive material is required to be so long that the thermoelectric conversion element 100 and the thermoelectric conversion element 200 do not thermally interfere with one another. However, it is possible theoretically to set the length within a range from small lengths of several micrometers to several hundred kilometers.
The thus-constructed heat transfer circuit system serves as a system where a heat-absorbing portion (i.e. a negative thermal energy source) and a heat-generating portion (i.e. a positive thermal energy source) are disposed an arbitrary distance away from one another so that these two positive and negative thermal energy sources may be used independently of one another.
When a current is supplied from the external direct-current power supply 300 (Vex) to the circuit system shown in FIG. 10, an endothermic phenomenon and an exothermic phenomenon occur at the both ends of the thermoelectric conversion elements 100 and 200 due to the Peltier effect. It is thus confirmed that the Peltier effect is effective in the construction where the thermoelectric conversion element 100 as the heat-absorbing side and the thermoelectric conversion element 200 as the heat-generating side are provided independently of one another. Moreover, it is confirmed that, in this case, reversing the direction of the supplied current results in inverting the endothermic phenomenon and the exothermic phenomenon at the both ends.
FIG. 11 is a schematic diagram showing a circuit system for confirming the Seebeck effect where the external direct-current power supply 300 is removed from the circuit system of FIG. 10, i.e. a thermal energy to electric energy conversion circuit system. In FIG. 9, it is confirmed that, when a temperature difference of about 80° C. is imposed between the end of the thermoelectric conversion element 100 and the thermoelectric conversion element 200, that is, between the joining member d103 and the joining member d203, an electromotive force of 0.2 millivolt is generated between the terminals from which the power supply is removed.
It is confirmed that the Seebeck effect holds also in the construction where the thermoelectric conversion element 100 as the cooling side and the thermoelectric conversion element 200 as the heating side are provided independently of one another.
In the circuit system shown in FIG. 11, the length of the conductive material is adjusted (within a range from small lengths of several micrometers to several hundred kilometers as necessary) so that the thermoelectric conversion element 100 and the thermoelectric conversion element 200 do not thermally interfere with one another. A portion of the conductive material is cut to provide output voltage terminals. One end of the thermoelectric conversion element 100 (the joining member d103) and one end of the thermoelectric conversion element 200 (the joining member d203) are disposed under different temperature environments. The temperature difference between the temperatures T1 and T2 in the respective environments, T1−T2 (or T2−T1), is maintained finite. Thus, it is possible to convert thermal energy existing in a different environment directly to electric energy, and to serve as a power source.
The Seebeck effect serves to convert a temperature difference directly into electric energy. This effect can be obtained at least by ensuring a distance with which a relationship of T1>T4 (or T1<T4) holds. Therefore, it is necessary to ensure a distance with which the thermoelectric conversion element 100 and the thermoelectric conversion element 200 do not thermally interfere with one another.
Patent document 1: Japanese Patent Application Publication No. 2003-92433.
However, such a circuit as described with reference to the schematic diagrams of FIGS. 10 and 11 requires an external direct-current power supply 300 for long distance thermal energy transfer, or requires terminals for obtaining an electromotive force in conversion from thermal energy to electric energy. When the conventional technique as disclosed in patent document 1 is proposed, the use of energy with the Peltier element and the Seebeck element is unidirectional. For example, there is no technical teaching of constructing a recycling system to recycle energy once converted into thermal form, foreclosing the associated external power supply, and reducing the accompanying noises in parallel.
However, it is desired in the future to use thermal energy so as not to cause global warming and environmental destruction, and to avoid the use of energy due to the provision of an external power supply in parallel with recycling. Moreover, in order to protect surrounding environments, it is necessary to reduce actively noises. This is a major required challenge in developing the technique to use thermal energy in the future.